


Rat Of Unusual Circumstance

by wasthatafanfic



Series: Ontological Inertia [2]
Category: Teenage Mutant Ninja Turtles (TV 2012), Teenage Mutant Ninja Turtles - All Media Types
Genre: Body Horror, Mutation, Of Rats and Men
Language: English
Status: In-Progress
Published: 2018-03-07
Updated: 2018-07-25
Packaged: 2019-03-28 05:46:03
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 6
Words: 13,581
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13897557
Author URL: https://archiveofourown.org/users/wasthatafanfic/pseuds/wasthatafanfic
Summary: Casey Jones is not having the best day.First Irma crashed his and April's 'date', Giant monster rats attacked the city, then he got kidnapped by the Rat King, And things are looking like they're only gonna get worse from here.





	1. Chapter 1

**Author's Note:**

> Yes I chose that title because I was thinking about The Princess Bride.  
> The Rat King was ready to test his newest formula, what if he got the chance? And what if Casey was his unlucky test subject?

Casey Jones was afraid of rats.

He had been since he was a little kid, something he couldn't really remember involving a neighbor kid and poorly considered life choices. 

So now, trapped in a cage with the often unconscious Irma dangling above an army of both regular and monstrous rodents alike cheering on their blind, desiccated master. He wasn't sure things could get much worse.

But as The Rat King got his monologue on, the pit in Casey's stomach dropped lower and lower

"That's right Aristotle, every time one of my rat people bites a human they will infect them. Causing the mutation to spread, and SPREAD until every human in this wretched world transforms into one of us!"

The mental image alone was enough to very nearly have him losing his lunch in his hockey mask.

"What's that you say? The serum isn't perfected? What do you mean?!"

Casey was more then a little sure he didn't want to see what The Rat King and his pet were looking at.

"Well, not every experiment can be a success. But this NEW serum WILL work. Perhaps we should test it."

Then the Rat King's blind bandaged eyes locked onto their cage and his rigor mortis grin widened.

"You're right Aristotle, she IS the perfect test subject"

Irma went down again in a dead faint to the Rat Kings grand amusement.  

Now Casey was the first to admit he wasn’t Irma's biggest fan but there was no way he was about to let something so horrible happen to her and he was more then ready to do whatever was needed to keep himself between that nutjob and her.

To his grand relief it wasn't something he'd have to try because only moments later all shell broke loose as out of nowhere what looked like a massive spilled ice cream cone came flying to throttle the unsuspecting Rat King. Within minutes his royal nutjob was gone and Casey was free, and he, April, and Irma were freeing the rest. Once the human prisoners were safe the fight was still going strong and he was right there, fighting alongside his friends, hoping wherever Splinter had dissapeared to he was doing better then they were.

The worry distracted him, and one of the monstrous mutants hip checked him across the room, up onto the platform the Rat King had been using for his experiments. He hit the table, upending it and landing in a heap on the ground again. 

A sharp pain radiated out from his side and shakily he yanked the syringe from where it had embedded itself in his flesh. Warmth was already radiating out from the injection site edging rapidly toward burning. He could feel himself being pulled to his feet and his arm dragged over a supporting shoulder keeping him upright, Donatello had him, and waved April away. 

"You get everyone to safety! We got this covered."

April eyed them worriedly, but a tired smile crept onto her face as she nodded 

"You always do."

Suddenly everything was starting to hurt, Casey's head was throbbing like his skull was trying to explode, his ears were throbbing, his skin was covered in goosebumps that felt wrong and painful and for some godawful reason even his tailbone ached.

"I dun feel so good, D." He slurred, He was starting to feel feverish 

"I know Case, it's gonna be ok though, I'm gonna get you out of here."

"Yeah D, you got this, you always fix evr'thn" Donnie was having to take even more of his weight as he couldn't seem to support it himself anymore. Donatello held the empty syringe he'd retrieved tighter in his grip. He really hoped Caseys confidence in him wasn't misplaced.

* * *

For April, getting back to the lair was a long and drawn out process. 

There were the prisoners to lead back to the streets, Then diverting any suspicion about her or mysterious green figures anyone may have noticed while escaping. The cops thankfully were easy enough to distract and dissuade from looking too closely into her involvement. The worst part was overhearing one officer ask an EMT "What about the nutjob's test victim?" and receiving a sad shake of the head and a quiet "Bastard never had a chance." That sure got her in gear to see how Casey was holding up.

 It was a bit of a hassle to get back into the sewers, as if every manhole cover had been cordoned off for blocks. A smart move by the police force for sure but not much help if you were trying to get into the tunnels unnoticed. And once she finally did make it the normally peaceful walk left her on edge, every scratch and skitter making her feel jumpy.  But the only rats she encountered on the trip reacted to her normally, either watching her pass in disinterest or scrambling to get as far from her as possible.

A heavy atmosphere of worry seemed to tumble out of the lair as she approached and she was calling out before she was even through the turnstile.

"Guys?" A sour feeling was growing in the pit of her stomach at how quiet the normally noisey home was. "Master Splinter?"

Mikey popped up over the back of the couch and chirped a greeting, the tv turned low and lackluster interest being paid to the video game Raphael was playing.

"Where is everyone?"

Raphael didn't look up from his game but his shoulders tensed as he answered, obviously fighting hard to hide his own agitation.

"Donnie's in his lab and Fearless is helpin Master Splinter with Casey in the spare room."

"We got kicked out." Mikey supplied, explaining Raph's terseness.

"And Casey is he-?"

That finally got Raph to pause and look up, the angry front draining to reveal his own worry as her words pattered off, unable to finish the question.

"We don't know, he was still okay last time I saw him but-" the mood tanked another few degrees as he found he couldn't finish the sentence either.

The lab door slid open with a snap and Donatello came rushing out, head low staring at the screen of some device in hand as he fast walked toward the bedrooms.

"Donnie!"

"April!"

The purple turtle flailed, device leaving his hands and having to be snatched out of the air again, at the surprise of her "sudden" appearance.

"Donnie, how's Casey? Is he gonna be okay? What's happening?" She knew she was bombarding him with questions and no spaces to answer but they all seemed to spill out in one go.

"I-I heard a cop talking, he said" her voice hitched "he said the guy the rat king experimented on last he - he didn't - he-" The words caught in her throat and it was all she could do to keep from crying.

Donatello took a deep breath, gaze shooting from her to the spare room and back as he made sure his own voice was as stable and sure as he could manage.

"Right now, he's okay. We're doing everything we can to make things easier and keeping tabs on how he's doing. Everything that can be done, is. It's gonna be okay." 

The deep breath he'd taken in seemed to escape April, his assurance enough to ease her fears and bring some confidence.

"Actually, that's part of why I was coming out here. Raph, can you and Mikey sneak back into the Rat King's hideout and get me some pictures of his formulas? It should help if we know what modifications he made to the mutagen." Something seemed to occur to him; "Oh, April, got a favor to ask you too, think you could go home and grab some stuff for us?"

* * *

Casey Jones was not doing so hot.

Well, that wasn't true in every sense, because he was currently spiking a fever that was dangerously high. He was fairly certain parts of him had by this point literally burned away, especially the point at his side where the needle had gone in. A hollow feeling like he was slowly disenigrating into ash and spreading to other parts of his body, hands and feet and ears especially.

Periodically something cool would press against his forhead and soothing words would filter through the haze bringing him some modicum of relief, but e could never quiet focus enough to figure out who it was or what they were saying.

His skin felt like millions of little pinpriks were pushing their way up through his pores, course hair spreading in uneven clumps across his body. There was an electric agony down the length of his spine, like it was being yanked from his body tailbone first. 

His head wasn't fairing much better. He swore there was a sound his jaw made as it felt like it was stretched and reformed, sinuses drawn out to match. 

 His face was soaked with tears and he clung to the hand that had pressed into his like a lifeline thanking silently anyone who would listen when he finally blacked out.

* * *

Getting out of the sewers and back again proved to be just as much of a hassle as it had been to start with, Police cordons harder to avoid when trying to spot them from below, but she made it out and back again with minimal fuss, just a lot of wasted time.

This time the lair had been not only silent but empty to boot, she would have panicked if that oppressive miasma from early hadn't dissapeared with it.

As it turned out, everyone had crowded into the spare room that she herself had spent a number of weeks in avoiding the kraang.

Donnie met her at the door.

"I got the stuff, is he-?"

"He's fine, well he's not in permanent pain or dying, fines probably a relative term all things considered."

April glanced past him and his family to the lump of blanket on the bed which seemed to currently be in a heated argument with Raphael.

"Come on Casey you're bein a big baby!"

The red masked turtle was tugging at the blankets edge and she realised its occupant must be doing everything in their power to keep it from moving.

"No, I said I'm not coming out from under here! Now let go!"

The blanket edge yanks out of Raph's hands and the whole pile settles with a pointed *whump* as every edge is tucked in and under, turning Casey into a blanket ball.

"You realize we were literally raised by a rat right?" Donnie added, eyeing the blanket ball and motioning toward the parent in question, regardless of the fact Casey couldn't see it. "You're not gonna freak us out or anything."

A hand was gentley placed on his shoulder as Splinter quietly pointed out 

"I do not believe it is us your friend is worried about, as you put it, 'freaking out.' "

Donnie tsked and turned his attention now to April 

"He couldn't possible think APRIL woul-" A soft squeeze cut him off and a pointed tilt of the head finally made the penny drop; Casey was the only person Casey was trying not to let freak out right now.

Mikey was looking between the Caseyball and Splinter and back again with a look of slowly dawning realisation.

Donatello was just about to suggest they should maybe all give him a bit of space, regardless of the fact he himself was itching to give him a once over to make sure everything had translated alright, when April pushed past them all and plopped onto the bed, nudging into him as she did.

"Come on Casey, we've all been super worried about you! We just wanna make sure you're okay." She nudged him again "Coommee ooonnnn. It can't be that bad."

More grumbling from the blanket ball and a quiet desperate whine of "but I have a tail." Which drew an eye roll from all but two of the rooms occupants.

"April is, literally, the only one here without a tail. You'll have to do better then that."

April shot them a look mouthing 'you guys have tails?' Leo shrugged and mouthed back 'tiny ones'.

The grumbling stopped and the blanket stilled and gave a defeated huff.

"Fine…but I'm gonna get dressed first so get out, and when I come out, no jokes!"

They let him be to have a few moments to himself to process and get dressed, Master Splinter having the forsight to have him remove his clothes before the mutation could damage them and Donatello having the sense to have April bring some that would probably fit his new proportions, knowing he wouldn't be comfortable in the same level of dress the turtles were.

Casey Jones was reaching the exact same conclusion they both had and was regretting his preference for skinny jeans, because there was absolutely no way he could fit into them anymore. The replacements April had bought were too big but were at least managable, and as he started to put them on it hit him why he'd been handed a pair of scissors as his friends had left, tails not working too well with pants and all. His shirt and hoodie miraculously still fit though and he slid them on with no small amount of relief, he resisted the urge to yank the hood up as far as he could before steeling himself to rejoin them in the living room.

They all held their breath as the door was pushed open, a pair of fur covered ears were perking up slightly as he noticed them all staring at him, devoid of the tufts at the tips or gashes Splinters had. He'd done his best not to look at himself  while changing, completely unwilling to see for himself how he'd been altered and the new ears folded back flat against his head as he asked nervously.

"How bad is it?"

Which of course meant Raph had to screw with him.

"From your ugly mug? It's an improvement."

Casey's eyes narrowed, like his voice they had remained unchanged, to glare daggers at his best friend and the shit eating grin the turtle now wore and an insult match sparked up between them.

His fur seemed to be a smudged mix of greys and blacks and Donatello wasn't the only one it occurred to that the black smudges on his face were surprisingly close to the way they'd learned he tended to paint his face under his mask. With big blotches over each eye, one down the center of his muzzle, and a blob from either side of his mouth smeared back along his cheeks.

Donatello was also glad to notice that while Casey did seem off balance, most likely from the new tail that looked to be shorter than Master Splinters and which the junior vigilante was starting to hold curled slightly upwards at the end so it didn't drag on the floor, none of his movements seemed pained or stunted. That seemed like a good sign that the irregularly drawn out mutation hadn't caused any unexpected damage or deformations.

April must have been worrying along the same lines because she cut the argument short.

"How are you feeling though? Does anything hurt or - I dunno anything we should worry about?" 

One last glare at Raph and he paused to take stock. Giving a shrug and stopping himself from scratching behind his newly placed ear with his newly clawed hand (which he stared at for a second as it hit him that he'd definitely lost fingers)

" I'unno Red, everything feels, like, super weird. But I guess nothing hurts? Nothing worse then like, being sore after practice or nothing"

His ears twitched as he spoke and he frowned, making his muzzle wrinkle humorously in displeasure "Okay the ear moving thing is super annoying." The hoodie was flipped up to pin them to his head.

"You get used to it." Splinter pointed out blandly, one of his own tilting up slightly as he spoke.

* * *

"So what now?" 

They'd settled into the couch of the sunkin living room, a few slices of pizza forced onto the newly mutated rat because as Mikey pointed out 'thats gotta take a lot out of you dude'.

Casey shrugged at April's question and eyed his slice uncertainly. He had an entirely new mouth, he wasn't entirely sure how he was talking normally much less if he could manage eating without difficulty.

"Not worryin' about that trig test tomorow, that's for sure." 

Raph snorted, Leo frowned, April rolled her eyes, not a full round of reactions but good enough.

"Well, obviously you're welcome to stay here 'til we can get this fixed." Leo pointed out, something occured to Casey and his ears perked up as he turned his attention to Donnie.

"Yo D! Arn't you like already workin on a cure for April's dad? Shouldn't be that long right?" He took an experimental bite of pizza and was pleasantly surprised to find chewing no more difficult then usual as Donatello did his best to look anywhere but at him.

"Uuuummm, that's not quite how it works."

The ears dropped again 

"Whaddaya mean."

"You didn't get mutated just with mutagen Casey. the Rat King, he did something to it first. I havent even figured out normal mutagen it's gonna take time to figure out what those changes did...and how to undo it."

The pizza slice fell from Caseys hand as a look of utter horror crossed his face accompanied by a shocked intake of breath, he shot up from the couch and nearly fell  as he jolted away from them all with a shouted expletive.

"Don't freak out, it's not that bad, you'll like hangin out with us I swear!" Raph knew this was all a shock but this reaction seemed a bit much.

"No that's not-! That Rat King guy! He said - he said he made it so it'd spread! Guys what if I'm, like, contagious!?"

His reaction suddenly didn't seem nearly as over the top with THAT particular revelation and four sets of eyes stared back with equal worry.

The fifth set however, gave a dismissive roll.

"You don't think that's the first thing I checked? He might have finally gotten the whole rat mutant thing right but he completely screwed up the viral part, you're clean."

Casey collapsed into the closest beanbag chair with a groan of "ohthankgod."

Mikey patted his head comortingly, and not at all to see if that fur was soft like Master Splinter's nope not at all.

"Hey, some good news at least! And, noticed you've got front teeth now, that's a plus right?"

A confused glance up at the orange masked turtle and Casey tested the inside of his mouth with his tongue. His teeth were sharper now, and they spread across a longer area, and just as Mikey had said the front four he'd lost ages ago to hockey were miraculously back in place.

"Huh, yeah I guess that's pretty cool." Everything about his body felt just a little bit off, and every movement brought that feeling to the surface, but already he could feel himself starting to adjust and that was somehow comforting. "Maybe this won't be too horrible, might even be kinda fun!"

They were starting to relax, Leo winning the definetely-not-staged for the sake of arguing argument with Raphael over putting on Space Heroes and Mikey was passing him another slice to replace the one he'd dropped (which Mikey had eaten himself, couldn't let it go to waste after all) When the first cords of 'We Will Rock You' filled the lair.

April dug through Casey's discarded sports supplies and passed the still ringing cellphone to him as he stared at it with slowly mounting horror.

He stared at the ringing phone and then at his friends and in a small worried voice announced:

"It's my  _ **dad**_."

**Notes for the Chapter:**

> In case anyone is worried Casey's dad isn't gonna be any of the current canon versions, No abusive alcoholics coming up I swear.


	2. Chapter 2

**Summary for the Chapter:**

> Trauma is a hell of a drug and emotional shock is a wild ride  
> Casey finally starts to process whats happened to him and the consequences coming his way

**Notes for the Chapter:**

> Amazing art commissioned from Turtle-Trash on tumblr of Rat mutant Casey jones  
> https://turtle-trash.tumblr.com/post/171714167959/two-commissions-for-buttons-n-bobbin-one-of-a

Casey Jones was very pointedly NOT looking at his cellphone, which was slowly vibrating its way across the table with the umpteenth call in the last few hours.  He instead was staring intently at the turtle anatomy poster on the wall, tail curled around into his lap where he was fiddling absently with it in what was probably going to develop into a nervous habit.

When Casey had categorically refused to answer his dads repeated calls, looking like the phone was ready to bite him if he got too close to it, Donatello had decided he'd instead have to endure a quick exam to make sure he was alright.

"You should answer that." April muttered, not for the first time, perched on the tables edge watching them both as Donnie looked him over.

Casey didn't even look at her, just gave a dry "Nah." and continued to sit quietly as Donnie did... something. He honestly hadn't been paying attention and only knew his arm was being twisted this way and that  by the purple masked turtle who periodically paused to scribble notes.

"Hey, how're you feeling?" Donatello cut in before April had the chance to lay into him, he could see a powerful lecture about worrying his father building up and Casey was in no shape to handle that.

" 'M fine."

His tone was dull, still staring blankly at the wall, ears flat and didn't even twitch when they spoke to him, he wasn't fine.

"Not...numb, or anything?"

The way his gaze shot his way was all the answer he needed and he tsked worriedly.

" _THAT_ would be shock. You kinda had a super traumatic experience today and all that adrenaline is finally wearing off and it's all hitting you at once."

"Great."

The grey and black smudged rat muttered, he'd stopped toying with his tail and it curled back behind him again,  ears drooping to the sides now instead of pinned flat back against his head.

"You just need some rest, and some time to process all this. You'll be okay."

To Donatello's surprise as he offered up words of comfort that pink tail curled around his green leg, a bit under his knee, and he was about to make a joke when it occurred to him Casey didn't realize he was doing it, unconsciously seeking out comfort while his attention was elsewhere and decided to let it be.

The phone started vibrating again and April had to catch it before it could attempt to launch itself off the tables edge. She stared at the steadily mounting message count.

"...casey..."

"I _can't_ Red." The emotionless stare was gone and his posture had crumpled along with his expression, which looked like he was fighting hard not to cry. The lab suddenly feels very very large and the three of them very very small.

"I've met your dad, he's great, the worst that's gonna happen is he's gonna get a little mad at you over the whole vigilante thing. He'll sure be a lot less worried about finding out about _this_ then he will be about you just _disappearing."_

"Yeah? And how do I explain this" he motioned to his rodentness, "Without everything else?! The mutant stuffs one thing but we got evil ninja's and freakin' aliens trying to kill us **_constantly!_** How do I tell him all that? How do I just drop all that in his lap? He's been worried enough about me and my sister since we lost mom how do I-" His voice cracked and he trailed off, burying his face in his hands as he lost the battle with his emotions.

They were saved from the awkward situation by April's phone going off this time.

"It's my aunt."

"It is getting late." Donatello pointed out, casually sliding the tissues off a nearby cabinet and setting them on the table next to Casey.

"Yeah... I'd better go before she really starts to worry."

She didn't want to leave, wanted to help her friends through this, but she couldn't bring herself to cause cause her aunt any more strife.

"That backpack I left in the guest room, it's got all the basics me and Donnie could think of. We can figure out anything else you need tomorrow if you want. Oh, and Raph snores like super loud once a night, it's weird but you get used to it"

"Thanks Red..."

She was turning to leave when he caught her elbow.

"Hey could you... can you text my dad for me? Like, tell him my phone died? and..." He searched the room like the perfect excuse was hiding on a post it note slapped onto one of Donnies experiments, an ear perking up as he reached the right white lie.

"That I went camping with Marcus? He'll be super mad about not asking first but it'll at least buy me the weekend to figure out what i'm gonna do about -" He motioned to his rodential self "-this."

April looked less then sure about the wisdom of this course of action but nodded, already tapping out the text in question for him as she headed for the door.

They watched her go, the *slide thunk* of the lab door sounded flat and hollow in the large room.

Donnie sighed.

"It _is_ late, and you need rest. Let's get you to bed."

He only put up a waning resistance, grumbling about being 'scienced to sleep' when the turtle lectured him about emotional shock and insomnia and needing the sleep for recovery. But he did go and crashed as soon as he'd hit the sheets and blessedly didn't dream at all.


	3. Chapter 3

**Summary for the Chapter:**

> Casey would really rather not be dealing with any of this so early in the morning, but a rat boys gotta eat.

Casey really _really_  did not want to get out of bed.

Mostly this was so he could pretend that yesterday was little more than an unbelievably vivid nightmare.

But the minute he was awake enough to realize he didn't want to be yet he was also awake enough to be acutely aware of every strange, different thing he could feel about his new body.

The feeling of a tail wrapped around one fur covered leg, the feeling at the base of his spine when it moved along with his shifting, a wide rounded ear that was too high on his head pinned against the pillow, the uncomfortableness of a damp nose shoved into fabric, and the fact he felt like he knew _exactly_  where both the pillow and blanket were specifically because of how they pressed against his whiskers.

Honestly none of that was quite enough to draw him out from his cocoon of warmth. What finally did it was his stomach reminding him he hadn't eaten anything since the stale movie popcorn the day before.

With a lot of whining and grumbling he dragged himself out of bed, blanket and all, continuing to grumble about how cold the concrete floor was and how his newly shaped feet felt like he was constantly on tip toe and trudged his way to the kitchen.

* * *

Raphael was splayed half across the kitchen island as Casey shuffled in, the turtle looking intent on dragging a few more moments of sleep kicking and screaming from the morning as Michelangelo cheerily busied about the kitchen making breakfast.

He was greeted by a joking "It's aliivveee!" from Mikey who was happily cracking eggs into a pan.

"Figured you'd be sleepin more, since you went through so much yesterday. I know I would if I could get out of training!"

Casey shrugged from under his blanket cloak and slumped into a stool across from Raphael, explaining himself with a groggy and muttered

"Got hungry."

"Great! I'll have breakfast served up in just a sec, you'll love it! Right Raph?"

"Mmmnnrrr." he didn't even bother lifting his head, the attitude didn't seem to put his baby brother off in the slightest because he cheerily announced while giving the turtles shell a pat.

"Ignore him he gets Hangry"

"I do not!"

"Ssuurreeee."

Casey chuckled and settled in to watch Mikey cook, under his blanket an ear twitched. A weird noise he only just barely registered tickling at his hearing.

"What _is_  that?"

He pulled the blanket down and the ears twitched at their own accord trying to pinpoint the source of the strange sound, a sort of humming moan.

Mikey hummed questioningly, not the noise but Casey finally zeroed in and stared at it's source.

It took a moment for Raphael, chin on the counter-top and eyes half lidded staring at nothing as he was, to realize he was being stared at.

The thrumming stopped abruptly as he sat up straight and glared in return and testily demanded explanation with a terse

"What."

"Was that you?"

Mikey ducked between them to deposit plates of scrambled eggs, five total, across the island top.

"Was WHAT me?"

"That weird, like, hummy noise?"

As the orange turtle deposited the final one in front of himself he leaned his elbow on the table and asked

"What this one?"

A similar thrumming hum moan came from the smaller turtle and Casey stared at _him_  now.

"THAT! What's up with that?!"

The brothers looked at each other, appearing mildly surprised.

"Wait, you seriously never heard us do that before?"

Casey shook his head, distracted only slightly by how he could feel his wide ears flopping ever so slightly as he did.

'It's just something we do when we're hungry. We’ve done it when you and April were over before."

"Well, I never heard it before."

"And…April's never mentioned it either."

Mikey's expression had turned to awe as he muttered this, the realization their human friends had been missing a regular part of their communication kind of blowing his mind.

"Dude."

So apparently he had super rat hearing now, that was a thing. Casey wasn't exactly sure how to handle that.

He turned his attention bake to the scrambled eggs in front of him, In the handful of weeks since he'd made friends with Raph he'd seen the orange masked turtle make and consume some of the grossest concoctions but man was Raph right, the guy could make some awesome scrambled eggs.

* * *

Casey didn't feel like sitting and watching his friends morning training, he considered vegging out in front of the TV but the lair felt eerily quiet without the normally raucous brothers. So he retreated to his borrowed room to take stock.

All his vigilante gear was laid out on the bed for inspection as he went over what was and wasn't still usable.  
Some of the stuff didn't really matter how he'd changed. Hockey sticks, pucks, bats, blocker, even the spray paints. Though he wondered if missing his pinkie fingers would mess up his aim when throwing them, that was going to take some getting used to, along with the fact he _was missing fingers_  which kept hitting him anew every now and then. It'd also make his gloves weird to wear. Maybe he should sew off the missing finger so it couldn't get in the way? Didn't want the empty fabric flopping around.

His pads should all work fine, home made tazer too, though his shoes and custom skates wouldn't work with the new shape of his feet. It weirded him out the extra bend in his legs, the new angle they seemed to rest at. Donatello had explained what he'd at first thought was a second, backwards knee was actually the equivalent of his human ankle for the newly digitigrade legs and that he was now  walking on his toes with heel kept up in the air. Between that and the weight and motion of the tail he constantly felt like he was going to fall over. Splinter had insisted that feeling would pass fairly soon.

Casey looked the shoes and skates over, maybe he could get Donnie to help him alter them to work with his new feet? It would be worth a shot.

Experimentally he'd pulled his mask on, it sat comically at the end of his muzzle and he sighed sadly, there was absolutely no way he'd be able to wear it now, well other then leaving it up on top of his head, that was an option. His face paint wouldn't be doable anymore, although he sure didn't have to worry about being recognized, no way anyone would think to connect a grey and black rat mutant back to his family.

His thoughts drifted to the phone still sitting on the table in Donnie's lab and he slumped, thinking about all the unanswered texts and voicemails within. At best he only had three days to figure out what to tell his dad, or a way to disappear from his families life that wouldn't completely destroy them. None of the options he could immediately bring to mind were especially palatable.

Everything from the last few days was suddenly weighing on him with renewed ferocity and he felt exhausted. Mikey had been right he _did_ need more rest. So with a quick shove that sent his equipment to the bedside of the head he curled up and drifted off into a fitful nap.

* * *

Lunch was…interesting.

Casey Jones stared into the open freezer with a mix of surprise, confusion, and concern.

"That…is a cat…made of ice cream."

The cat in question mewed lovingly and began grooming itself, not seeming at all distressed by its current state.

"Yup." Donatello confirmed bluntly from behind him

"Is that the stray April brought over?"

"Yup, sure is."

"How does that even happen?"

"Mikey's fault."

The grey and black mutant rat teen gave him a disbelieving look and Donnie could only shrug in return.

"Apparently, right before the whole Rat King thing kicked off, It licked up some of a test batch of retromutagen I was working on that Mikey dropped - you guessed it - Ice cream into and…that…happened."

Michelangelo's beaming smile to Casey's left faltered only for a moment before he blew a raspberry at his older brother and brightened right back up.

"Hey! That means you guys'll share a mutation day! That's so cool! Isn't that awesome my pretty kitty?"

"What exactly is a mutation day?"

This time Leo took up the explanation.

"We don't have real birthdays, so we celebrate the day we were mutated instead, it's only a thing for us really."

"Master Splinter said we can keep her! She's Neapolitan an I'm gonna call her Ice cream kitty an ICK for short an isn't she just the best!

He continued cooing and coddling his sticky new pet, which soaked the attention up with glee, and left Casey giving the rest of the turtles in the kitchen an expression that successfully conveyed his current feeling of 'wtf' on his new face.

The other three turtles could only offer shrugs, they didn't get Mikey sometimes any better than anyone else.

"I guess that’s something to be thankful for." Raphael pointed out as he used a sai to open the poptop on his soda and earning a glare from Leo for misusing his weapon "At least my brother didn't turn you into a _desert_ …"

Casey nodded absently, still watching Mikey lavish the goopy thing with attention

"instead of a giant opossum."

He froze stock still, and turned very slowly to glare at the very cocky looking turtle.

"I. am not. An opossum."

The smirk widened and Raphael took a casual sip of his soda.

"Ya sure look like one."

If pressed, Casey wouldn't have been able to put into words why this rankled him so much. He didn't even _like_  rats but dangit if he was gonna be stuck as one he was at least gonna be called the right thing.

"Big words for a giant frog."

Donatello groaned, knowing full well where this was going and begged through a face palm.

" _Please_  at least take it out of the kitchen."

Neither boy acknowledged him but when Raphael went in for the tackle the fight conveniently went right out the kitchen door and rolled all the way to the pit that served as their living room where Splinter was currently enjoying his stories.

"WAIT!"

The wrestling match came to a screeching halt before he even needed to say anything as Casey fumbled with his borrowed, too big jeans that kept threatening to slip down on him.

Grumbling as he fussed to make to make them fit at least somewhat properly around his altered legs and tail about how annoying they were.

"Why do you think I wear robes?" Splinter commented dryly, switching on the subtitles so maybe he could keep up with the plot.

Casey considered the elder rats attire for a moment, then his own oversized jeans with the poorly cut hole in the seat for his tail.

"Nah. I'll figure it out. Yo D! What are the chances we could get my skates to work with these?"

He stuck a paw up in the air and splaying his toes (and pushing down the panic that hit him again at the re-realization he was missing some of them)

Donatello rolled his eyes at the display, but did consider the question.

"Probably, it'd take some doing though. Come on, lets see what we can do."


	4. Chapter 4

**Summary for the Chapter:**

> Time to start getting used to some things.  
> And whats up with that rumbling?

So Casey squeaked now. That was a thing he was going to have to learn to accept and get used to till he was fixed up.

They'd spent most of the afternoon mocking each other while they redesigning his skates and from there had done some tune ups on the rest of his equipment and then moved onto some tossing around ideas for more, and were finishing off with helping with some of the techy turtles more recent projects.

He hadn't even noticed he was doing it for ages, Donnie hadn't mentioned anything while weird little frustrated * _eekeekeek*_ noises slipped out of him as he struggled with an amazingly stubborn bolt on an engine the purple masked turtle had scavenged and had been putting off scrapping for parts. Casey probably wouldn't have noticed at all if the socket wrench hadn't slipped yet again and he'd _shrieked_  at it, freezing as it caught up to him that the very not human sounding noise had come out of him, and that it wasn't the first.

"Have I been making weird noises the _whole_ _time_!?"

He demanded of the currently thoughtful terrapin who only glanced up from his blue prints long enough to make sure he hadn't hurt himself then went back to focusing on whatever he was sketching out.

"Not the whole time, just every now and then."

"Why didn't you say anything?!"

A shrug "Wasn't bugging me, I talk to myself when I work sometimes too."

"That wasn't talking."

"Venting then, it's really not a big deal. Hey are you any good with torque ratio's? I'm having trouble with this."

Casey groaned. He absolutely did not agree on this being 'no big deal' animal instincts hijacking him without him even being aware of it seemed like a very big deal to him, but Donatello was so nonplused and already on to the next topic that he realized it was a pointless battle.

"Yeah I'm pretty good on 'em," he finally conceded, abandoning the impossible bolt and joining the turtles side "Where's the problem?"

* * *

Beyond the frustration of mostly smaller instincts sneaking up on him (after the squeaking thing he'd been watching tv with Raph and casually scratched an ear using the claws on his _back foot_ , and he was still trying to figure out how he felt about that one) Casey was, to his surprise, getting used to the changes in his body a lot faster then he  figured he would. By that evening he'd gotten his balance back, the extra weight and swing of his tail (he'd already started shifting from thinking of it as 'his' instead of 'the') and the tip-of-his-toes way his new legs made him walk was already starting to feel nearly as comfortable as his normal gait had. A bit of roughhousing with Raph in the evening and he was starting to feel pretty confident that even if he wasn't completely back he was already on the way.

But a worry had been steadily gnawing at the back of his mind as the day went by. Donatello had been able to reassure him that The Rat King had been unsuccessful in making his rat mutation contagious, but that wasn't the only risk his current state posed.

After all, the psychopath had managed to turn Master Splinter, arguably one of the toughest dudes Casey had ever met, against his own sons. The ninjitsu master had been able to fight off his control, but what hope did Casey have?

"That is not something you will have to concern yourself with."

The sureness in Master Splinters tone had surprised him when he brought his fears to the wise old rat master, and the confusion must have shown on his face.

"The problem has been… dealt with. Your mind shall remain your own. At least in that concern you can rest easy."

The grim look on his face made it clear what he meant by 'dealt with' and Casey could only think to answer with a small "Oh, good." as he was offered a comforting pat on the shoulder before the elder rat went on to other tasks.

* * *

April stopped by that evening, dropping off the stuff Casey had thought to ask for over the day with a deadpan announcement of

"Honestly never expected to need to break into a friends home to steal them pants." 

He was sure glad she had though, because among the options she'd snagged he found a pair of cargo shorts that were considerably more comfortable then the jeans he'd been making do with. And with a bit of tailoring (courtesy of Raph, whom his siblings insisted had quiet a talent for it, which from the work he presented Casey was inclined to agree with them) they even fit comfortably around his tail.

 [[Rat!Casey by Rhi-Draws-Things](https://turtle-trash.tumblr.com/post/171714167959/two-commissions-for-buttons-n-bobbin-one-of-a)]

The weight of the slowly dawning revelation of having to stay underground and out of sight had him feeling antsy and uncomfortable and he just wanted to be out and away from everything.

It didn't take too much prodding to convince April to go roof hopping with him, especially after he made it clear he'd be going whether he agreed to or not, and simply didn't bother asking anyone else if it was okay before he did.

He wanted to test out the skates Donnie had helped him with, see how he handled the rest of his equipment, Shake off some of the claustrophobia realizing his existence was now mostly to be relegated to underground, possibly sneak in a bit of one on one time flirting with April with a side of hopefully taking out some of his mutation frustration on unwary purple dragons.

Of course that quickly spiraled into yet another bizarre adventure when they stumbled across a bunch of Krang and the discovery of their portal device.

While he considered his first run in with the Krang a success, double points for winning the fight despite being unpracticed in his new mutated body, once they'd gotten their find back to the lair it took barely ten minutes after explaining what the thing was for all of them to go charging through, Casey couldn't believe he'd let Raph trick him into letting the red turtle be first through.

The night passed in a blur of craziness.

The hall of portals was mind blowing, even if seeing the alternate versions of themselves was weird it was also mildly comforting that other-reality him looked to be human, if he found out this was some sort of forgone conclusion he might have freaked. And Donnie was right, that _was_  a nice jumpsuit on Other-April.

Getting separated hadn't been part of the plan. Him, April, and Donnie being captured even less so. Although dang if he wasn't pleased with how he'd done against the krangdroids that'd had them at gunpoint, using his new tail to send one krangdroid tumbling even as the other met the business end of his taser.

Being swallowed by a freaking _space worm_  was DEFINITELY not part of the plan, and he was suddenly very very glad for his new tail when after a considerable amount of struggling it was the only part of himself he could manage to get free, because once he did he managed to use his newest appendage to maneuver his cellphone out and up enough to attempt a rescue call which he was just as amazed as April that the call even managed to make it through.

The wait for rescue had been agonizingly long. Especially since he was pretty sure he could _feel_  the things stomach acid eating away at his fur, he prayed he didn't end up a _naked_  rat on top of everything else. But rescue did come and he could now unfortunately say with complete certainty that being thrown up was even grosser then being eaten.

If Donnie's comment about him being the 'worlds largest hairball' stuck he was gonna be so pissed. But after the whole 'saving him and April from being sucked into dimension x with the last of the space worms' thing he could probably let a couple jokes about it slide.

* * *

Once they'd finally finished saving the day and made it back to the lair Casey was as good as dead on his feet (paws? He kept forgetting he had paws now) He was once again glad for his tail because the counterweight was the only thing keeping him from just face planting the second they were through the turnstiles.

The alien worm puke had hardened into his fur and was making everything uncomfortable and itchy.

A spot on his arm was being particularly annoying and he instinctively started to move to bite at it only to be interrupted by a hand gently pushing his arm back down.

Casey shot Master Splinter a bleary and confused look and was met with a simple explanation of

"You'll give yourself bald spots."

He squinted, judging the words and the tone.

"That sounds like some first hand experience advise right there."

Splinter was suddenly very interested in looking anywhere but directly at Casey and answered evasively

"Advice that should be headed, regardless."

Casey was too tired to laugh at the mental image of a patchy furred ninja rat but he did manage a small grin.

Meanwhile Mikey, who against all odds was still his usual bouncing bundle of energy, was badgering Donnie and April for details about their end of the night's adventures while disjointedly filling them in on what had happened to him, Leo, Raph, and Master Splinter.

Halfway through though, he stopped short and all his attention suddenly zeroed in on the resident red head.

"I almost forgot! I was gonna ask you somethin. Hey April, what do you hear when I do this? "

Casey's ears flattened as Mikey started making another of those odd noises, this time a sort of rolling churr that immediately drew the attention off his three brothers and Casey noticed even Splinter twisted an ear their way in notice.

But April didn't react, just sat expectantly before glancing at the rest of them in confusion and asking

"What noise?"

The orange masked turtles eyes got very large and he pointed like she'd just been caught at something.

"GUYS! HUMANS CAN'T HEAR TURTLE!"

Things devolved  from there, with Mikey babbling a scattered explanation of what they'd realized that morning and every one else trying and mostly failing to keep up and figure out what exactly he was on about.

Casey took this as a good time to take his leave and stumbled toward his borrowed bedroom.

Too tired to even consider a shower to get the dried alien puke off, he didn't even bother with clothes or equipment removal and just collapsed straight into the bed, passing out completely within seconds.

* * *

His second morning waking up as a rat mutant had him considerable less uncomfortable about his ratness, but only because all his discomfort was currently laser focused on how very much his clothes and vigilante gear were not conducive to a good night's rest. Not to mention the gunk that had permeated everything he wore, rubbed off on the bedding, and was  currently cemented into his fur.

Just everything needed a thorough washing, but his stomach reminded him food was the preferable first step.

He groaned as he leveraged himself out of bed and peeled off his gear, the clothes would have to wait till he'd been fed.

There was a crick in his neck, a kink in his tail, his left ear was sore from it flipping inside out while he slept and staying that way all night.

He was more then a little surprised to find all four brothers in the kitchen, seated at the center island with what looked like some kind of board game spread over the whole thing and Leo apparently leading whatever was going on.

"Yo Casey! You got a good night sleep this time! We only just started dude, we can still roll you a character if you want!"

Michelangelo was wobbling with so much excitement on his stool Casey was worried he might fall right off it, but with the unreal chaotic finesse he was coming to expect from the hyperactive turtle he remained upright.

"Yeah, didn't shower or nothin just blacked out. Kinda regretting it though-"

He picked at one of the clumps and was greeted by four rather disgusted expressions, he couldn't blame them.

"Yeah, I know, I'm just snagging something to eat then I'm not leaving your bathtub till this is allllll gone. So thanks for the invite Mikey but I think I'm'a have to skip out."

A smattering of relieved sighs and understanding shrugs as he circled the counter island to the fridge.

And jumped as he opened the freezer because he'd totally forgotten about their weird cat. But Ick passed him the toaster waffles so all was forgiven.

"What're you guys playing anyway?"

"Mazes and Mutants, found it topside. We figured with everything we just went through we could justify at least a little downtime."

"They are forcing me to play this." Raph announced blandly, but was immediately tackled by his baby brother

"Aw come on you're havin fun! You're just grumpy cause you got stuck with the Barbarian Dwarf!"

Casey plucked his waffles from the toaster and ate them plain as he watched Raph struggle to get Mikey off, he just wanted to get to that bath as soon as possible.

"Used'ta have a buddy who played that, never got a chance though. Maybe I'll get to play the next round! But I call the elf."

Mikey whined, slumping off Raph's shell, but ultimately conceded if it meant he'd join them.

He was already feeling better with something in his stomach, now that bath was calling to him. 

Donatello was nice enough to pull out the pain pills when he mentioned how sore he was and snarked as he handed over a glass of water.

"Casey for all our sake take all the time in there you need, I think April left some of her good shampoo and some other stuff from when she had to stay with us. And yes we do, it's the hall to the left just past our bedrooms and the detergent and dryer sheets are in the cabinet above, the one on the right. Master Splinters really the only one who uses it."

"Thanks dude. You guys enjoy your game, I'm gonna go attempt to de-space-puke my fur."

Just as he was about to leave the kitchen he leaned back and with a wicked grin called out

"Hey Raph?"

"Yeah?"

"Don't ccrriitttt~"

He barely dodged the dice that were chucked at his head.

* * *

It took a distressing long time and a whole lot of scrubbing to get himself clean. Fur was woefully good at holding onto grime when it'd had a night to dry in. He went through half the bottle of shampoo and probably owed someone a new brush but after a _lot_  of elbow grease he did manage to get well and properly washed up.

Then he was faced with the ordeal of drying off. He tended to just wiggle a towel over his hair and let it air dry the rest of the way but he had a feeling his grey and black smudged coat was much better at retaining moisture.

After he'd soaked through the first towel and was still distressingly damp and he started searching for alternatives, eventually settling on a hairdryer he came across.

echnically it worked

It left him a giant fluff ball, but it did work.

With nothing left clean but a towel he was really glad the guys seemed to have disappeared.

Master Splinter informed him they'd taken their game out into the sewers, then suggested a dryer sheet would help with his current fur issue.

So there would be no mocking, and it left him a bit more comfortable in only having a towel to wear while he dragged his sheets, clothes, and any fabric pieces of his equipment into the laundry room.

As he sat on top of the dryer, waiting for the third load to finish for its next round of decontamination and still fluffier then he'd like, he let his attention turn to the cellphone he'd finally retrieved from Donatello's lab.

The resident genius had thought to plug it in for him, so it wasn't dead. But that meant he didn't have any excuse not to look at the message count that had blessedly trailed off shortly after April had sent his excuse for him. That meant his dad had bought it and only sent a few more telling him he should have asked first and remembered to charge his phone before hand and he'd better be safe and have fun.

But that pretense wouldn't  hold up to scrutiny much longer and the idea of just disappearing, of his dad not knowing what had happened to him…

His heart was in his throat as the line rang and he struggled to silence the worried squeek's the new rat part of him wanted to make.

Relief flooded him as the answering machine picked up, if his dad had picked up he wasn't sure he'd have been able to keep from hanging up out of pure panic.

*Beeeep*

A deep breath.

And he dove in.

"Hey dad? It's Casey, uh, I know April said I went camping without asking first but - but that wasn't the truth. Something - Something kinda happened. And I'm okay But - uh - but it kinda, I'm a little different now. I'm sorry I lied and I'm sorry I didn't tell you right away but I didn't want to freak you out. I gotta wait til it's dark but I'll come home tonight and I'll explain everything just- just don't freak out when I do okay?" It all came out in a rush and he hoped it was mostly understandable as he finally inhaled "I love you dad, and tell Chloe I love her too."

With that he hung up the call and slumped back against the laundry room wall and wondered if he was making the right choice

**Notes for the Chapter:**

> Got 'The Manhattan project' and 'Monsters and Mutants' into the same chapter, little pleased about that.  
> And yes Splinter was warning him about chewing a bald spot from personal experience, happened early in his mutation from a mix of stress and living in the sewers just making him feel constantly icky and itchy before he got used to it.
> 
> Next up Casey's finally gonna go home and face whatever reaction his mutated self will bring~


	5. Chapter 5

**Summary for the Chapter:**

> A less than pleasant homecoming

"You sure you don't want one of us to come along?"

The red masked turtle was leaning against the doorframe of Casey's borrowed room as the vigilante-turned-rat anxiously prepared for his evening.

He didn't answer right away, ears twitching with uncertainty and a nervous eek sneaking out of him as he considered, but eventually he shook his head.

"Naw, It's fine dude.  April should be more then enough backup. I'll be fine…it's fine."

He was anything but fine. The idea of facing his family, revealing his recent mutation and all the dangerous secrets that went along with it, ones he'd been so very carefully keeping from them.

He felt utterly terrified.

The red masked turtle gave a disinterested shrug and tossed out a "Your funeral." With a dismissive wave over his shoulder as he left that had Casey a bit stunned by the rude attitude.

Getting to his apartment was nerve wracking.

He never noticed how crowded his apartment complex was.

People were everywhere, jostling him in the elevator, bumping him on the front step, pushing by in the halls, and every glance every sideways look was another close call of being discovered.

He stood hunched in the hall, an oversized hoodie borrowed from the turtles that was helping to hide his prominent rodent muzzle.

April went in first, Casey's improved hearing _just_ able to make out her muffled voice through the closed door as she tried her best to soften the coming blow.

"Hey."

The door had open just enough to allow April to pop her head out and give him the universal 'come on' head jerk.

And he was in the kitchen. Hood pulled far forward, shoulders slumped, tail and paws hidden under oversized jeans, and  clawed hands shove deep into pockets.

April was still talking, but Casey wasn't really listening, focusing more on keeping his breathing steady  and human and not letting any anxious squeaking escape him as his father asked questions and April answered for him.

"Where's Chloe?" He cut in, something about his sister's absence making him uncomfortable in an entirely different way then the rest of the situation.

"Somewhere safe." The clipped tone kept him from asking from what, afraid of the obvious answer, safe from _him_.

It was just him, April and his father then. The kitchen felt cold and claustrophobic and dim in an entirely unfamiliar way.

He was pulling back his hood, revealing fur and whisker and ears, and his heart clenched painfully as his father jerked back with a gasp as he laid eyes on his altered son, disgust clear in their depths.

His father's hands gripped his shoulders tightly and Casey couldn't push him away as he shook him.

"What were you thinking? How could you do this to us? Put us in danger like this?!"

With each question his finger dug in harder and Casey's panic mounted, April watching stonily a few steps away but making no move to intervene. This was his battle alone.

Instincts, human and rodent alike, surged up as sharp fingers jabbed his arms, words burned like bile.

Fight or Flight, attack or run, flee or defend.

And with no way out that only left one other option.

Sharp teeth came down on soft flesh and his father cried out, reeling away and clutching his injured hand to his chest, April rushing to the man's side and eyes wide in shock and horror.

He was stunned, frozen, horrified that he'd harmed family in such a way. But as he stepped closer, apologies already spilling and stuttering from his mouth, April blocked his path.

"What have you done?" her horrified tone cutting him to the bone as his father hunched further over his wound, back to his son.

"I'm sorry I didn't mean to I swear I never-'

"What Have you _done_?"

Casey's father echoed as his shoulders twitched and shuddered, voice turning rasped and warped and Casey realized that something was very _very_ wrong.

April, still trying to get a look at his hand, didn't have time to pull away as he grabbed her yanking her forward with and biting hard on her forearm.

Now Casey could see his father's features twisting and distorting. Eyes a murderous red as fur blossomed painfully across his body, bones crunching and scraping as it stretched into a wrinkled deformed snout, jagged teeth jutting from his maw.

April cried out as her hands became clawed and fur raced up her own arm, her body spasming as her own transformation began.

"Nononono this cant…Donnie he…"

Before his eyes both parent and friend contorted painfully into creatures less like himself and Splinter and more like the giant rat monster that had menaced the city only days before.

"This cant be happening"

His legs collapse from under him as they both rounded on him accusing and Scratchy and inhuman voices screeching.

"WHAT HAVE YOU DONE!?!"

There was nowhere for him to go, nothing that he could do. Only stammer apologies and beg for their forgiveness. But there was no forgiveness, only the infection, and soon it would spread and Spread and **_SPREAD_**  until everyone he cared about, his friends and family and the world beyond, would all be twisted into feral monstrous creatures.

He was sobbing now, huddled against the kitchen wall as the rat monsters continued to demand an answer from him.

He didn't know, didn't understand how this could have happened.  Donatello had run tests and checks and assured him that he wasn't some walking biohazard. How could this have happened?

"Don't you understand child?" 

There was no kitchen wall at his back now, replaced by a tall blindfolded and emaciated figure that smirked down at him with rotted teeth.

Casey's heart jumped into his throat and pounded there even harder with panic so that he could only just barely squeak out a desperate "But you're **_dead_**."

The Rat King laughed and it sounded like a dry crypt "Yet you're still here my boy." a rotting hand patted him condescendingly between his folded flat ears and he was horrified to find he couldn't move, couldn't pull away. "And now thanks to your work this wretched world will be mine and all the people in it beautiful rat creatures under  _my_  control."

There was no turning away from what had happened, what he caused, what he had _done_.

He was surrounded on every side by the monsters he had created. Not even Splinter and the turtles could escape the effects of the virus Casey himself had spread, now joining the monstrous snarling freaks that had once been April, his father, and like the final twist of the knife his beloved little sister. All turned into grotesque mockeries of rodential mutations that shrieked and snapped at him as standing over them all, cackling gleefully, was the King that controlled them.

He couldn't move, his body was no longer his own. The maniacal laughed now echoed within his head as well as without and the only thing left to him was his desperately swirling panicked thoughts surging to more and more frantic depths.

_This couldn't be happening I'm so sorry this wasn't supposed to happen this can't happen please don't let this be happening please please stop plea-!_

 

 

 

_**THUD THUD THUD** _

 

 

 

Casey's eyes snapped open, his chest rising and falling rapidly with short frantic breaths as reality filtered back into his mind. He was curled into a tight ball on his borrowed bed. The blankets twisted and curled around him in a makeshift nest, another little push from his new instincts. His tail was tucked almost to his nose, knee's to his chest, and fur sticking to him with fear induced sweat.

He hadn't gone home yet. None of it had been real. Just a bad dream.

A very very bad dream.

Shakily he pulled in deep even breaths, trying to steady the crazy speed of his pounding heart.

There were still hours till he and April were to head to his place,

Another set of thuds that he belatedly realized it was knocking at the bedroom door, and it finally registered that the first set had been accompanied by someone saying something through the door but he wasn't sure what it'd been.

This time the door opened, and Donatello peaked in. A worried expression on his purple masked terrapin face.

"You okay in here?"

He wasn't, and it took him too long to murmur out an unconvincing " 'M'fine." for there to be any chance that he'd just let it go.

"What happened?"

Before he could argue further that no, really, he was just fine the light had been flicked on (momentarily blinding him) and the resident medic was at his bedside poking, prodding, and peering at him.

"Did something start hurting? That fever didn't come back did it? I just checked your levels there shouldn't be any further changes happening with your mutation but this is a new variation so-"

A bit of flailing and Casey was finally able to pry Donatello off from inspecting how his pupils were reacting to the light, pulling both hands down and holding them in place with a huff.

"Nothings hurting and nothing started changing again! Chill gaptooth I'm tellin you I'm _fine_."

Donnie's nose scrunched at the teasing nickname but didn't rise to the bait.

"No you're not _fine_  It sounded like you were in _pain_. So what is going on then, because somethings up."

He faltered, the tilt of his rounded ears giving his emotions away till he finally accepted there wasn't an easy way to brush things off.

" 's no big deal Dee, Just a bad dream." his ears were pinned back and he suddenly couldn't quite look at the turtles face.

Donnie inspected him critically.

"Must have been some dream, you sure you're okay?"

"Yeah, fine, swear. Sorry for buggin you."

Haltingly, Donnies weight shifted on the bed, willing to let him be but unsure about it. He did pause however and give a laugh.

"Until you come waking me up at oh-god-why'thirty because your monster movie marathon has you convinced carrots are going to eat your brain you're not even close to bugging."

One ear perked in amused curiosity.

"Mikey?"

"Mikey. And twice just in the last month."

 He was almost in the clear, Donnie just about out the door and willing to brush the whole thing off as nothing.

Anxiety had him worrying at the end of his tail again and as his gaze went down to his fur covered and clawed hands the nightmare came surging back in all its gruesome glory.

"Dee, wait."

He paused, one hand on the door.

"The Rat king, that stuff he wanted to do… the whole virus thing…"

Donnie shrugged "Yeah he totally screwed that up, lucky he got the mutation part stable before your dumb ass fell on it." The smirk he shot Casey's way fell quickly as he noticed just how freaked out he looked as he quietly asked.

"You're sure?"

Welp, he didn't have to ask what Casey's nightmare was about anymore.

"Yeah, I'm sure. You want, I can show you the negative results. Can even run a few more tests to be totally sure."

While the idea of being poked at and sampled more wasn't especially attractive, the image of his little sisters grotesquely mutilated form was even less so.

"Okay, yeah, lets do that. Check everything over before April gets here." Before he risked bringing anything more then his own messed up self home.

The usual insults and teasing were kept at a minimum as Donatello carefully reran every test and check he could think of to make absolutely sure there was no chance Casey's nightmares could become a reality.

**Notes for the Chapter:**

> Scared ya'll for a second didn't I?  
> I hope some of you started to suspect something right off when Raph was such an ass.  
> I tried something new for the nightmare part trying to make it more disjointed since its a dream, how'd I do?


	6. Chapter 6

**Summary for the Chapter:**

> Lets try this again.

**Notes for the Chapter:**

> After Casey's nightmare it's time to face the music for real and find out how his family reacts to this whole mutant rat situation.

"You sure you don't want one of us to come along?"

The red masked turtle was leaning against the doorframe of Casey's borrowed room as the vigilante-turned-rat anxiously prepared for his evening.

He didn't answer right away, ears flattening and breath hitching as his earlier nightmare surged up into the forefront of his mind.

He shook his head trying to dislodge the after images.

There was none of the dismissive bluntness of his dream as Raph gave an accepting shrug.

"Yeah, you're right, you an April got this. But if you _do_  need a hand remember we got your back, ok?"

Casey nodded lingering anxiety still turning down the edges of his features, and didn't expect when Raph  leaned back to glance along either side of the hall before darting forward and giving Casey a supportive hug.

"Everything's gonna be fine, so stop stressing."

He of course followed this up with a much more in character grumble of  "Never tell _anyone_  I did that." once he'd released the rat mutant.

He must have been freaking out bad if even the generally physically unaffectionate tough guy of the team had considered such support a necessity, and while it was a surprise, it had also helped.

The edge now taken off his bad dream induced panic he was able to offer up a smirk and a punch to the arm.

"Yeah you're right dude, and I wont tell anyone you're actually a big old softy."

Raph sputtered and Casey snatched up his hoodie as he raced past before he could get a retaliatory strike in, laughing the entire time.

* * *

"So, you hear Raph do that three am super snore thing?"

April asked as they trekked their way through the sewers toward the manhole by Casey's apartment complex, the easiest way to get there without being seen.

He snorted, Casey kept forgetting she'd had to live with them for a bit when the whole 'the krang are trying to kidnap me' thing had first happened.

"Naw, passed out too hard the last few nights. Did hear somebody makin lil whistling noises though."

Now it was April's turn to laugh, having to smother it so it wasn't too much.

"That's Donnie! I think it's cause of that little gap in his teeth. You can always tell when he actually gets some sleep cause of it."

He refrained from commenting that the sound was kinda cute.

"Don't tell him I said so but it's kinda cute." April commented absently and Casey settling for a noncommittal noise in response to her voicing his thoughts, sometimes it was weird how she could do that.

Everything about her body language was relaxed and casual. Like they were on their way to her place to study instead of on their way to possibly the most stressful conversation of Casey's life.

They were taking the sewers to get there, he was wearing his hoodie and cargo shorts (leaving his vigilante equipment at the lair of course, April was still going in first but on a different path then Casey was. No borrowed oversized hoodie to hide in, no nerve-wracking slinking through crowded hallways, no lurking awkwardly outside his own home.

The further they got from the details of his dream the more His panic returned to a more reasonable level of anxiety.

April shouldered the heavy manhole cover open and popped up into the alleyway first, checking the coast was clear before Casey joined her.

They were silent as they parted ways, April out to the street to head in by the front door while Casey would go in through his own bedroom window.

"Hey," His gaze jerked back to the alley entrance where April had popped back around the corner " It's going to be fine, you got this!"

Her warm, supportive smile disappeared around the corner again.

He lingered in the empty alley probably longer than was wise. Staring up at the bedroom window that he'd snuck out of countless times without a care.

He skipped the fire escape ladder, Instead he kicked off his shoes and put his new paws to good use, claws allowing him to scale the brick wall with surprisingly little difficulty and going over the railing.

For all that it freaked him out Casey had to admit some of the benefits of this whole rat thing were pretty darn cool.

One last check of his phone to make sure there were no _**ABORT MISSION**_  messages and he popped the window lock with an ease born of years of practice and slid inside his bedroom.

* * *

His room was exactly as he left it.

Which made sense, considering it had only been the weekend, but it sure felt like a lot longer

He hesitated, he could hear the muffled sounds of the city from the again closed window he'd just come in through, muted conversation filtered through the walls from the direction of the living room, his little sister singing to her stuffed animals filtered from her bedroom in the other direction.

It all felt so normal, and for a moment he was caught between the comfort of it and the fear of how it could all go wrong.

The living room voices started to draw closer and his heart jumped to his throat, leaving him internally  scrambling for what he should do. Ultimately retreating to his bed and sitting anxiously perched on the edge nervously worrying at his tail.

When the door swung open, revealing his dad's tense frame and concerned features still turned partway over his shoulder to April, Casey couldn't breathe as he waited for that gaze to land on the strange creature that was his son.

But there was no jerk , no disgusted flinch, no gasp.

Instead the concerned crease unknit from Mr. Jones brow, shoulders relaxed, the worried frown turned up into a relieved smile. He crossed the room without hesitation and the rat mutant was scooped up into a tight hug which he returned with equal ferocity

Even with the air being squished out of him by his dad's embrace he felt like he could breathe for the first time in days.

Over his dads shoulder April was absolutely beaming at them, shooting Casey two thumbs up and eliciting an eye roll from him.

"You scared the _crap_  out of me disappearing like that!"

"Sorry dad."

One last big squeeze and he pulled away to give his son a proper once over.

"So…this is a thing…"

Casey ducked his head a bit in embarrassment, nose giving a twitch and ears flattening to the sides as he offered a muttered.

"Yeah."

Mr. Jones looked caught between confusion, concern, and amusement.

"You know when I gave you 'The Talk' this isn't what I meant when I mentioned hair in weird places."

April went bright red, groaning into her hands as she shook her head in disappointment and Casey burst out laughing. She supposed he had to get his sense of humor from _somewhere_.

As their laughter faded the concern returned to his expression and he asked seriously.

"Casey, are you okay?"

Casey fidgeted, not just firing off a knee-jerk reassurance but actually giving the question the consideration it was due.

"I…Yeah, mostly? Like, it hurt when it first happened and it's kinda super weird but its not that bad. Some of its kinda cool even." He considered the tail he was currently worrying at in his hands. "And my bud and his bro's are helpin me out, like get used to it an stuff."

"April mentioned them. These are your friends who are - turtles?"

Casey snorted at the look on his dad's face as the man tried to brace himself for the weirdness he now knew was coming.

"Yep mutant ones, and Ninjas, and their dads a rat."

Mr. Jones eyed him.

"That, uh, that doesn't have anything to do with this does it?" motioning to his ratness.

April and Casey were quick to end that line of reasoning, filling him in on the Reader's Digest version of the Rat King, Master Splinter's disdain for him, how the martial arts rodent had put an end to his reign (even if they didn't know the how of it), and had readily offered Casey their spare room for the duration of his mutation.

"Not so sure how I feel about that," Mr. Jones admitted "you staying with folks I'm only just hearing about and never met"

This was April's cue to reassure him

"I had to stay with them for a couple weeks a while ago there is no safer Place promise."

Mr. Jones didn't look especially convinced but a little more of the stress tensing his frame drained away at her reassurance.

"When you didn't come home or answer my calls, I thought the worst. 'Specially after what your sister went throu-"

"WHAT HAPPENED TO CHLOE!?"

Casey shot up at the mention of his baby sister; posture going rigid, ears straight, hackled raised, and teeth bared, every inch of him was suddenly on the defensive at the implication of a threat as he demanded "What happened?! Is she okay? Where is she!?"

"She's fine! She's fine, calm down."

He pushed Casey back down, ruffling the fur on his head as he did so for good measure before he explained.

To Casey's horror it turned out his baby sister had been disturbingly close by when Casey had been mutated, having been snatched by one of the Rat King's monster rat's like so many others, it was a wonder Casey hadn't seen her among the other caged hostages.

"You can imagine my relief when the pizza delivery kid showed up with her in hand, but then I didn't hear from you and I was worried they'd gotten you too." He eyed his rodent son. "I guess I wasn't too far off."

Casey was still too concerned to even look embarrassed.

"But she's okay? They didn't hurt her or nothing" A worrying thought occurred to him "Oh God, she just got kidnapped by a bunch of monster rats. I'm going to freak her out!"

Mr. Jones snorted.

"Considering with the pizza boy handed her over she was raving about how cool it all was and asked if we could keep one…"

April made a face remembering the how unpleasant the rat monsters had been.

"Seriously?"

"Seriously. Actually, she's been worried about you too." with no additional warning Mr. Jones turned and called out "Chloe! Casey's home!"

The swift pounding of small feet heralded the arrival of the youngest Jones.

"CASEY! Where have you been! You had me and daddy _scared_!"

She was already lecturing him before she even reach the bedroom door, stomping in all prim and proper in her dress and hairbow with arms crossed.

Only for her righteous fury to melt into confusion as she paused at the threshold.

Her gaze turned questioningly to her father, then April, then laser focused on the final furry figure as she puzzles him out inspected him.

Casey waited, frozen by her gaze and his own fear of scaring her.

Or worse, hurting her somehow.

Her head tilted slightly as she took him in and suddenly recognition lit in her eyes.

"Casey!"

The teen in question was rocked as the full weight of a gleeful six year old launched into his chest.

"Your fuzzy! Why are you fuzzy! You got whiskers! Is that a tail? that's so cool!!"

"Oh yeah, your family looks _terrified_ " April snarked as Chloe crawled all over him, inspecting his new form, and the redhead was rewarded with a pink tongue stuck out at her when his sister's attention was securely elsewhere.

"So," Mr. Jones brought their attention back to the topic at hand as Chloe continued to harass her big brother unabated. "About this whole stayin at your friends' thing."

* * *

"Captain Ryan! Look ouutttt!"

Yet another Space Heroes episode blared on the TV. Master Splinter sat on the couch, his sons scattered about the rest of the recess they called a living room. Donatello was curled around his laptop in the corner of the couch, furiously typing away at his newest theory on his retro mutagen, gaze flicking up to the tv every now and then to keep up with the plot. Michelangelo and Raphael were both sprawled out on beanbags. Mikey in rapt attention while Raph putting on a grumbling show of not liking the program _at all_ but was definitely watching from the corner of his eye. Leonardo was perched at Master Splinters side, excitedly explaining the show to his father.

A nameless red shirted ensign was vaporized right after warning Captain Ryan and being roundly ignored in favor of a showy frontal assault.

"This Captain Ryan seems a bit…enthusiastic about endangering his team."

This netted the elder rat mutant a lengthy theological lecture about the subtle undertones of the Captains  heroics and motivation, most of which sounded to him like a good it of projection on his eldest sons part.

Splinter chuckled to himself as he nodded along, glad to see his son so passionate about something other then training. Even if he didn't really get the show and preferred his soaps.

The peace was unexpectedly broken by the shrill ring of the cheese phone, Splinters ear twitching toward the dojo in alarm.

It was surprising to be receiving a call to begin with, especially since all four of his sons were all with him safe and sound.

"Oh shell," The almost curse had fallen from a very concerned looking Raphael "What if it's Casey?"

The thought had occurred to Splinter as well and he was tense with worry as he lifted the plastic cheese slice to his ear.

"Moshimoshi."

All four brothers were pressed almost in a pile just behind him, trying not to actually crowd him as they waited impatiently to find out what was going on.

"Hai April."

Four sets of eyes widened, definitely about Casey then.

"Ah, yes I understand."

Mikey started to whine, his silence lasting longer then he could handle, and Donnie slapped a hand over his mouth to keep him quiet.

"Yes of course, we will see you soon."

Calmly, Master Splinter returned the cheese slice to its dock and turned to the mound of anxiety awaiting news that was his sons.

"It seems that we will be having some additional company this evening. Casey's father wishes to meet us."

**Notes for the Chapter:**

> There is absolutely nothing in canon to support Chloe being Casey's little sister but the idea entertained me exactly because of getting to write the next chapter.

**Author's Note:**

> I live for comments, questions, and any feedback you might want to leave so don't hesitate I wanna know what you think!


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